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Motion control, S-curves and other stuff >> controlling lift with DC motor
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capt bullshot:

--- Quote --- I have to investigate what is the real source of that problem.
--- End quote ---
Good luck, I'm quite confident you're able to find the root cause.

Need 50kHz or not: No idea, except higher switching frequency allows for lower inductance. That particular motor indeed is pretty low inductance, so 20kHz to 100kHz looks appropriate for a rated 100uH / real 30uH. Not a big deal for modern MOSFETs.

Running the timer @ 144MHz: should work if the datasheet says so ;)

krisRaba:
Ok, problem solved and actually it was something stupid ;-) I forgot that value written to BDTR (DTG) register to set deadtime is related to timer clock  :palm: so after increasing clock frequency effective deadtime was decreased proportionally ;-) After increasing it as well power stage is cool as usually  :-/O
And signals from MCU looks ugly now.. but only with ground lead ;-) With spring ground connection on probe it is OK.

But I will think about decreasing gate resistors a little bit. Now 10R is used so small bannana shape is visible on gate charging and discharging. Or maybe I will add diode+resistor in parallel just to turn it off faster and keep slower turn on time because of EMI...

And what is most important current ripple significantly decreased with 50kHz PWM ;-) I wonder what will be the effect of additional chokes in serie, it should be even better ;-)
capt bullshot:

--- Quote from: krisRaba on October 24, 2019, 08:35:21 am ---Ok, problem solved and actually it was something stupid ;-) I forgot that value written to BDTR (DTG) register to set deadtime is related to timer clock  :palm: so after increasing clock frequency effective deadtime was decreased proportionally ;-) After increasing it as well power stage is cool as usually  :-/

--- End quote ---
Business as usual ;)


--- Quote ---And signals from MCU looks ugly now.. but only with ground lead ;-) With spring ground connection on probe it is OK.

--- End quote ---
Business as usual ;)


--- Quote ---But I will think about decreasing gate resistors a little bit. Now 10R is used so small bannana shape is visible on gate charging and discharging. Or maybe I will add diode+resistor in parallel just to turn it off faster and keep slower turn on time because of EMI...

--- End quote ---
I've seen higher gate resistances working just fine - depends on the MOSFETs and it's just the usual power dissipation vs. EMI tradeoff game   >:D


--- Quote ---And what is most important current ripple significantly decreased with 50kHz PWM ;-) I wonder what will be the effect of additional chokes in serie, it should be even better ;-)

--- End quote ---
Business as usual  :-+
krisRaba:

--- Quote from: capt bullshot on October 24, 2019, 09:20:47 am ---
--- Quote ---But I will think about decreasing gate resistors a little bit. Now 10R is used so small bannana shape is visible on gate charging and discharging. Or maybe I will add diode+resistor in parallel just to turn it off faster and keep slower turn on time because of EMI...

--- End quote ---
I've seen higher gate resistances working just fine - depends on the MOSFETs and it's just the usual power dissipation vs. EMI tradeoff game   >:D

--- End quote ---
Yes, I know. I have seen even 100R in ST BLDC controller ;) Worked well with 6-step but it was a tragedy when I was trying to implement sinusoidal driving and had to be reduced ;) So it also depends on control scheme and your needs. But I am also aware that high rise times look good on DSO but are your enemy in EMI ;) But on other hand additional inductance should add some slope ;) I have just checked that driver already has 5R of internal resistance for LOW TO HIGH transition and 0.55R for HIGH TO LOW transition so it is already asymmetric. I will leave that for further testing in the future ;)


--- Quote from: capt bullshot on October 24, 2019, 09:20:47 am ---
--- Quote ---And what is most important current ripple significantly decreased with 50kHz PWM ;-) I wonder what will be the effect of additional chokes in serie, it should be even better ;-)

--- End quote ---
Business as usual  :-+

--- End quote ---
I have added 2x 4,7uH in series with motor windings and just as expected, current ripple has been decreased. It is not enormous change, something about 25%, but always something is better than nothing  :-+ Does it mean that effective inductance of motor is about 37,6uH? I think so and it sounds quite realistic. It would be 36,5% of 103uH presented in datasheet and they were talking about 30-80% for calculations..
capt bullshot:

--- Quote from: krisRaba on October 24, 2019, 10:00:24 am ---I have added 2x 4,7uH in series with motor windings and just as expected, current ripple has been decreased. It is not enormous change, something about 25%, but always something is better than nothing  :-+ Does it mean that effective inductance of motor is about 37,6uH? I think so and it sounds quite realistic. It would be 36,5% of 103uH presented in datasheet and they were talking about 30-80% for calculations..

--- End quote ---

Yes, I'd agree using the same rough (and probably incorrect) calculation pointing to the ballpark range. Good enough for a plausible estimate.
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